Field
This disclosure relates to heating control systems, and methods for controlling heating systems. More particularly, the disclosure describes heating control systems, and methods of controlling heating systems, which use weather information to achieve energy savings.
Description of Related Art
Thermostats and Heating Control Systems
Conventional temperature control systems often use thermostats to allow the user to create predetermined set points for indoor temperatures. A thermostat samples the temperature within a structure, and calls for heat or cooling from a heating, cooling, or HVAC system. Thermostats are used with all manner of heating, cooling and HVAC systems; and the settings on the thermostat are usually driven by considerations for the comfort or safety of the occupants of the structure. The temperature in a structure can be managed by one or more temperature control system, and by one or more heating, cooling or HVAC system. Either or both of the temperature control system or heating control system can be stand-alone, or can be a part of a building management system.
Current thermostats can be programmable to allow set points to be programmed for specific times of day, and for days of week. These times and set points can correspond to when the user expects the building to be occupied, when the occupants are expected to be away such as during the workday, or when they are typically asleep.
More recently-developed thermostats can regulate energy usage in response to peak demands on the power grid. Such thermostats call for, for example, less cooling in a structure when the power grid is at peak usage, and some thermostats of this type are also able to sense whether a structure is occupied, and even further reduce power consumption during times of peak demand if the structure is unoccupied.
Other recently-developed thermostats use the future occupancy status of the structure to determine set points for the temperature of the space. For example, a thermostat can receive a signal via the internet indicating that an occupant will soon arrive at the structure, and adjust its temperature set point accordingly. In other cases, based on historical data regarding occupants' movement in the structure, a thermostat will predict when the structure will be occupied, and adjust its temperature set point accordingly. For structures which are regularly occupied, these technologies, alone or in combination, are both energy efficient and ensure optimal comfort of the occupant of the structure.
Outdoor temperature, or forecasts thereof, are currently used by numerous heating control systems in a variety of ways, for example: to merely display the temperature to users, to calculate mechanical heat lag (MHL) to determine when a system needs to be activated to achieve a target temperature by a predetermined time, to determine the thermodynamic properties of a building, to evaluate the efficiency of a heating system over time, as a variable in a demand response system which primarily shifts start and stop times, as a variable considered in a fresh air ventilation (FAV) controller, or as an indicator of how energized a boiler system needs to be to have the thermal capacity to heat a space.
Unoccupied Structures
None of the above-described thermostat functionalities, however, addresses the need for energy-efficient heating of unoccupied structures. According to the U.S. Census Bureau estimates, there were approximately 17.3 million vacant housing units in the United States as of the first quarter of 2015.
In colder climates throughout the world, such unoccupied structures are unnecessarily heated in order to prevent damage to the structure from cold, in particular from freezing pipes. Second homes, vacation homes, offices, any structures left unoccupied for extended periods, and even particular zones within a structure that are expected to have longer periods of time where they are unoccupied, can benefit from a system which will heat the space within the structure enough to prevent damage from cold, without unnecessarily heating the space. In these situations, the comfort of an occupant is not the objective; rather, a combination of energy savings and prevention of damage to the structure caused by the temperature is. Currently, the temperature in such unoccupied structures is usually set to a single pre-selected set point, and the space within the structure is kept consistently at that temperature. In colder climates, this pre-selected set point is selected because it will keep the space within the structure warm enough to prevent damage to the structure from cold, for example from freezing pipes. A typical fixed setting of 50-65 degrees Fahrenheit is often selected for such situations. (The lowest recommended setting, per the American Red Cross, as well as major insurance companies and others, is to 55 degrees Fahrenheit while buildings are vacant.) Such a setting is high enough to keep the unoccupied structure safe during periods of extremely low temperatures, when there is a risk of damage to the structure, for example from freezing pipes. Decreasing the indoor temperature from 68 degrees Fahrenheit to 55 degrees Fahrenheit (a difference of 13 degrees Fahrenheit) produces estimated savings of 39% in these unoccupied structures. (The U.S. Department of Energy estimates up to 1% savings on heating for each 1 degree Fahrenheit of setback for an eight hour period. Estimating savings for unoccupied spaces over a whole day would therefore mean 24 hours per day savings or 3% savings per 1 degree setback.)
In times of only moderately low temperatures, however, for example, when outdoor temperatures are 35-50 degrees Fahrenheit, a thermostat setting of 55 degrees Fahrenheit causes heating of the unoccupied structure which is not necessary to prevent damage. A further 15-20 degree reduction in indoor temperature set point (from 55 to 40 or 35 degrees Fahrenheit) could yield significant savings: approximately 45-60% of the estimated energy currently being expended to heat unoccupied homes. Therefore, a vast amount of energy is wasted worldwide. On most days, structures that are expected to be unoccupied for longer periods are kept much warmer than would be necessary to prevent plumbing and property damage.
In many unoccupied structures, the default temperature setting, and therefore the amount of energy used to heat the space, could be dramatically lowered if the thermostat in the structure could reliably and automatically adjust the thermostat set point upward when outdoor temperatures decline and the chance of damage from cold increases. Currently, heating control systems are not available with this functionality. There therefore remains a significant need for a method of controlling the heating of a structure which considers outdoor temperature and provides enough heating to prevent damage to the structure from cold, but without expending unnecessary energy.